From The Gemology Project
Revision as of 05:08, 12 September 2007 by Doos (talk | contribs) (addition from Chaman Golecha (id:93))
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search
Chemical composition ThCa2Si8O20
Crystal system Tetragonal
Habit Elongated, pebbles.
Cleavage None
Hardness 6 - 6.5
Optic nature Uniaxial -
Refractive index 1.560 - 1.596
Birefringence 0.001-0.008
Dispersion Low
Specific gravity 3.28
Lustre Vitreous


Tetragonal system.
Habit: crystals are elongated parallel to the optic axes. Massive as pebles. A rare crystalline non-metamict state of ekanite has also been found.

Chemical composition

ThCa2Si8O20: Calcium Thorium Silicate with radioactive elements present. Commonly Uranium, Iron, Lead also present. Metamict and rarer non-metamict ekanite has been found.



Green, dark brown, light brown, emerald green, also chatoyant, 4-ray, 6-ray varities also. Straw yellow when pure; dark red (due to inclusions).


Transparent to translucent.

Specific gravity

S.G. 3.08 (impure) and 3.28 - 3.36 (pure) generally 3.28


Optic Character: DR, Uniaxial negative.
Refractive index: 1.560 - 1.568 (may also be 1.590-1.596 or 1.573-1.572) Most commonly 1.596
Maximum birefringence: 0.001 - 0.008

Ekanite may test isotropic due to metamictization.


May show lines at 630, 658 nm


UV fluorescence: generally inert


Crystalline inclusions

Other properties

Radioactive; enough to activate a Geiger Muller Counter. Non-radioactive material also found. May test isotropic due to radioactivity.


Heat treatment to restore crystalline state.


Braziallianite: lower S.G.; R.I., D.R.


Geological occurrence:
Found as water worn pebbles; first in the gem-gravels of Sri Lanka. Also in glacial syenitic boulder.

Geographical locations
Ehiliayagoda, near Ratnapura in Sri Lanka; Also chatoyant, 4- or 6-ray also. Also at Mt. Ste Hilare; Quebec, Canada; Central Asia; Tombstone mountains, Canada (non-metamict ekanite).